The NFL and its players’ union are showing renewed interest in attempting to implement changes to the sport’s drug policies that would include players being blood-tested for human growth hormone, multiple people familiar with the deliberations said Wednesday night.

People on both sides of the negotiations said there was an increased willingness to try to find a way to overcome the remaining obstacles in the discussions and finish the long-awaited agreement. But all of them, speaking on the condition of anonymity because the negotiations were to stay confidential, cautioned that the talks remained fragile and a potential deal still could unravel.

“It’s been close before,” one of those people said. “We’ll see.”

The NFL season begins Thursday night in Seattle with the Seahawks, the defending Super Bowl champions, hosting the Green Bay Packers.

The league and the NFL Players Association agreed as part of their 2011 labor deal that players would be blood-tested for HGH. But the two sides had to agree to the details of the program for testing to begin, and that still hasn’t happened. They have been at odds at different times over the use of a population study to determine what would constitute a positive test for athletes the size of NFL players, and over the appeals process.

Most recently, the final negotiating obstacle was said to be whether or not NFL Commissioner Roger Goodell would resolve appeals of suspensions for violations of the policy other than positive tests. The NFL has appeared willing to allow a neutral party to resolve all appeals in cases based on drug-testing results, but to this point has not been willing to permit non-testing-related appeals to be heard by someone other than the commissioner.

HGH is on the NFL’s list of banned performance-enhancing substances but players are not tested for it.

The renewed push in negotiations was first reported by Profootballtalk.

According to people with knowledge of the talks, a deal between the league and union potentially could bring other changes to the drug policies, such as a higher threshold for what would constitute a positive test for marijuana; a shift of amphetamines from the performance-enhancing drugs policy to the substances of abuse policy; and prospective increased penalties in drunk-driving cases.

One person close to the situation said a catalyst for the latest change in attitude toward the negotiations was the four-game suspension given this week to Denver Broncos wide receiver Wes Welker for testing positive for a banned performance-enhancing substance. There were multiple reports that Welker tested positive for amphetamines. One of those reports said that Welker took MDMA, known widely as “Ecstasy” or “Molly,” laced with amphetamines.

Welker denied that to the Denver Post and told the newspaper: “I don’t do any drugs.”

The paper reported that Welker tested positive for Adderall.